Keep the 1911
I've had both 1911 & USP, which I consider the prototype for the HK45 (my opinion and my opinion alone).
They are vastly different in design, feel and operation, and if you only wanted some refinements on your S&W 1911, you might consider buying another 1911 with all the refinements you want already built in. The dominant decision factors (which are unknown to me) are 1. the use you intend for the pistol and 2. how much money you are willing/able to spend.
The last thing I would want to do is buy an "upgrade" pistol and realize I like it even less than the original. In any case, Good Luck!